Wildcard matching is a pattern-matching method that uses special placeholder characters to match one or more characters in a string. It is used in file names, search queries, access rules and command-line filters, where symbols such as * or ? stand in for variable text.
How wildcard matching works
Wildcard matching uses placeholder characters to compare a pattern against text when the exact string is not known in advance. The two most common wildcards are *, which usually stands for any sequence of characters, and ?, which usually stands for a single character.
The technique is simple, but its behaviour depends on the system that implements it. File shells, search tools, access-rule engines and command filters may all support wildcard syntax, yet each one can define separators, escaping rules and case sensitivity differently.
Where wildcard matching shows up
Wildcard patterns are common wherever users need flexible matching instead of exact equality. In file systems they help select groups of names, in search interfaces they broaden a query, and in policy or filter engines they can describe sets of paths, hosts, users or commands without listing every value individually.
That convenience is why wildcard matching is often treated as a usability feature, but it is also a control feature. A pattern that looks narrow to a human can expand far more broadly than intended if the matching engine interprets metacharacters, directory separators or empty strings in an unexpected way.
Wildcard syntax and matching rules
Wildcard matching is not a single universal standard. A shell may interpret a pattern one way, while a web application, firewall rule set or IAM policy language interprets it another way. The same characters can therefore mean different things depending on context, which is why exact syntax must always be read in the relevant product documentation.
Two details matter most. First, whether matching is anchored to the whole value or only a substring. Second, whether special characters can be escaped so they are treated literally. Without those rules, a pattern can accidentally match more data, more files or more actions than the author intended.
Why wildcard matching needs careful control
Wildcard matching can create security and reliability problems when it is used for access rules, path filtering or command selection. Overly broad patterns may expose files, allow unintended commands, or match sensitive resources that were never meant to be included.
It can also create false confidence during review. A rule such as user* or /app/* may seem precise, but the actual blast radius depends on how the matcher handles prefixes, nested paths, hidden characters and precedence with other rules. In security-sensitive settings, the safest interpretation is the one verified by the product, not the one assumed by the author.
Risk and Threat Considerations
Wildcard matching becomes risky when it is used as part of authorization, filtering, or command selection because a broader-than-expected pattern can expand access or affect the wrong target. Attackers may try to exploit that gap by choosing names, paths, or inputs that collide with permissive patterns.
Failure mechanism: The matcher treats a pattern as more general than the operator intended, or it interprets special characters, separators, or empty text in a way that widens the match set.
Impact: The result can be unintended file access, unsafe rule matching, bypassed restrictions, or accidental inclusion of sensitive resources in a control boundary.
Standards & Framework Alignment
This section maps relevant standards and security frameworks to the operational risks and controls described in this guidance.
NIST SP 800-53 Rev 5 and CIS Controls v8 set the governance and control requirements practitioners need to meet.
| Framework | Control / Reference | Relevance |
|---|---|---|
| NIST SP 800-53 Rev 5 | AC-6 — Least Privilege | Wildcard rules can widen access if patterns are too broad. |
| AC-3 — Access Enforcement | Wildcard matching often defines what an access policy will permit or deny. | |
| CM-7 — Least Functionality | Broad wildcard filters can expose or permit more functionality than intended. | |
| Recommendation — Review wildcard-based access rules under AC-6 to keep matches as narrow as possible. Validate wildcard policy behavior under AC-3 before using it to enforce access decisions. Constrain wildcard-enabled filters under CM-7 so only necessary targets are matched. | ||
| CIS Controls v8 | CIS-6 — Access Control Management | Wildcard patterns are frequently used in access control and filtering rules. |
| CIS-12 — Network Infrastructure Management | Wildcard filters can affect path, host, or traffic selection in infrastructure controls. | |
| Recommendation — Test wildcard-based rules under CIS-6 to prevent unintended authorization scope. Audit wildcard selectors under CIS-12 so infrastructure filters do not match unintended assets. | ||
Practitioner Guidance
What to watch for: Treat wildcard patterns as executable logic, not as informal text. Test them against real examples, including edge cases with separators, empty strings, and literal metacharacters, before relying on them in access rules or automation.
Governance implication: In shared platforms, wildcard usage should have ownership and review because a small pattern change can materially change who or what is matched. Prefer the narrowest pattern that still does the job, and require explicit escaping when literal special characters are allowed.
Related resources from NHI Mgmt Group
- What is the difference between hard matching and soft matching in identity sync?
- What is the difference between pattern matching and AI-native classification for sensitive data?
- What do security teams get wrong about wildcard redirect URIs?
- How can organisations prevent email mismatches from breaking user matching?
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Reviewed and updated by the NHIMG editorial team on October 29, 2026.
NHI Mgmt Group — the #1 independent authority on Non-Human Identity, IAM, and Agentic AI security. nhimg.org